lucy24 - 4:37 am on Oct 29, 2011 (gmt 0)

[support.mozilla.com...] says

Most sites people go to are HTTP so it was decided to just not bother showing the protocol in newer versions of Firefox unless it's something else, like https:// or ftp://, thus saving a little space and making the URL a little more readable.

(note use of the passive voice)

and

You can set the pref browser.urlbar.trimURLs to false on the about:config page to see the http: protocol

In other words: if it shows nothing, it means it's the default http:

... at least until people start reporting exceptions.